This Phase II application deals with non-invasive acoustic imaging of the nasal airway. Images of airway cross sectional area as a function of axial distance along the airway are reconstructed from amplitudes and arrival times of acoustic returns measured at the airway opening. Although this technology has been shown to be accurate, to require little or no subject cooperation and to have a number of diagnostic applications in nasal, pharyngeal and pulmonary airways, its broader applicability has been limited by unwieldy dimensions of the apparatus, which have hindered its use outside the research laboratory. In Phase I we developed a new theoretical approach that releases the acoustical constraint that had previously set the minimum possible length of the apparatus. Accordingly, this theory revealed a pathway for developing a compact apparatus. Unlike single-microphone systems used currently, this new technology is based upon a two-microphone measurement. In Phase I we successfully developed, implemented and validated this theory, associated algorithms and a prototype apparatus. Compared with present single-microphone systems this prototype was smaller by more than an order of magnitude and exhibited substantially improved measurement stability and ease of use. The objective of this Phase II application is to refine and package this next generation of acoustic reflection technology, as well as to explore and validate its clinical utility. The technology developed in Phase II will find diagnostic and screening applications not only in the research laboratory, but also in the doctor's office, in the ICU and in the workplace. Because it requires little contact time and little or no subject cooperation, this technology might become particularly useful in the pediatric clinic and the neonatal ICU.